Press roller, and method of producing same



United States Patent 3,031,206 PRESS ROLLER, AND METHGD 0F PRODUQENGSAME Robert K. Remer, Elgin, Ili., assignor of forty nine percent toRobert W. Hannah N0 Drawing. Fiied Dec. 31, 1956, er. No. 631,484 3Claims. (til. 154-43) This invention relates to rollers used in printingpresses. While primarily useful as inking rollers in offset printing andimpression rollers in rotogravure printing, the rollers of thisinvention may, to some degree, be advantageously employed elsewhere inprinting presses.

In the printing process, certain difficulties have been encountered dueto friction and static electrical charges. The problems arising fromsuch factors are particularly bothersome in the transfer of ink from areservoir to a printing blanket in offset printing and the transfer ofink from cylinder to a paper web in rotogravure printing.

In the ordinary printing press, the ink is placed in a reservoir orfountain and is conducted therefrom to the printing surface by means ofrollers. Some of these rollers are normally rubber-coated and others aremade of uncoated metal. This invention, insofar as it relates to inkingrollers, is concerned solely with those rollers which are normallyrubber-coated.

As the rollers contact one another and oscillate one upon the other,friction is generated which causes certain difiiculties resulting inpoor printing and costly roller damage.

Two types of friction, static and kinetic, result from the action of therollers upon one another, or upon another material, such as ink, incontact therewith. Static friction generates heat and electricalcharges. Kinetic friction causes surface wear.

The heat and electrical charges generated by static friction cannot bedissipated by ordinary inking rollers which are dielectric; thus, whentwo such rollers contact one another the electrical charge of eachattempts to transfer itself to the other. An electric arcing may resultwhen two rollers contact one another, and such arcing may cause theelastic filament of the ink to rupture, causing the ink to back-trackand mist.

Back-tracking of ink occurs when the ink pigment separates from the inkvehicle. The freed pigment is repelled by negatively-charged inkingroliers, and backtracks through the inking system, redeposi-ting itselfin the fountain or reservoir.

The misting of ink also occurs when the pigment sep rates from the inkvehicle. The pigment separated from the vehicle tends to fly from theinking roller and printing blanket causing a mist.

It is believed that at least some of the kinetic friction generated bythe action of the rollers upon one another is a result of theelectrokinetic or zeta potential of the rollers.

It is believed that most materials have a surface film of water.According to electro-kinetic theory, when two substances, such as waterand rubber are brought into contact, there is an adsorption of ions fromthe water onto the rubber surface, setting up what is known as aHelmholtz electric double layer.

The migration of the ions from the water to the rubber, results in alayer of negative charges in'water firmly fixed to the rubber surface,and an adjacent layer of positive charges lying in the water beyond thelayer of negative charges and movable with the water. The electrokineticor zeta potential is the potential between these two layers. Since suchpotential exists, and since the charges are immediately adjacent to oneanother, there is an attraction between the rubber and the water andthey are held together quite firmly at the surface of the rubber.

It is believed that inking rollers adsorb a certain 3,081,206 PatentedMar. 12, 1963 amount of ink on their surface during the course of normaloperation. I believe that such ink forms a Helmholtz double layer on thesurface of the inking rollers, and in respect to ordinary inkingrollers, the surface of the inking roller has an electrokineticpotential with respect to the ink.

Since in normal operation inking rollers are constantly in contact onewith another, the ink film becomes common to two rollers at their pointof contact, thus tending to bond together the two rollers, due to theelectrokinetic potential between the rollers and the ink film common toboth of them.

Ordinary rollers are not treated in any manner to counteract thegeneration of kinetic friction, and are subject to glazing, pitting andwear.

In rotogravure printing a web is coursed between a nip taken in animpression roller, which is coated with a resilient coating, such asrubber, and an etched rotogravure cylinder. The rotogravure cylinder,which is coated with ink, transfers the image to the web, the impressionroller acting as a support for the web to allow the image to betransferred thereto.

Static friction is caused as the web travels at high speed through thepress machinery, and such friction generates static electrical chargeson the web. When the web consists of newsprint, or other types ofuncoated paper, loose surface fibers, which are normally arrangedparallel to the surface of the web, are caused to assume a positionperpendicular to the surface of the web. However, when the staticelectrical charge is removed from such a web, the fibers will reassume aposition parallel to the surface thereof.

When a web whose surface fibers are arranged perpendicularly to thesurface thereof comes in contact with a rotogravure cylinder, wicking, aprinting imperfection, may result.

Wicking is characterized by areas of the web which should be uniformlyprinted upon being devoid of ink in small areas. As the free end of afiber which is perpendicularly arranged from the surface of the webcontacts a rotogravure cylinder, the fiber acts as a wick, and conductsthe ink from a small area of the cylinder. When the cylinder contactsthe web, that area from which the ink has been removed by the fiber isdry, and so cannot transfer an image to the web.

Ordinary impression rollers, being dielectric, cannot conduct the staticelectrical charges from the web. Impression rollers which are made inaccordance with this invention are electrically-conductive, and whenequipped with a proper ground, allow the electrical charge from the webto be dissipated.

Kinetic friction is generated bythe action of the web over theimpression roller. It is believed that the web has a surface film ofWater which is not ordinarily apparent. The impression roller adsorbs agiven amount of the water film, and a Helmholtz electric double layer isformed in the same manner as on the inking rollers.

This kinetic friction causes the surface of ordinary impression rollersto glaze, pit and wear. When an impression roller becomes glazed orpitted, or has become quite worn, the press must be shut down while theroller is replaced.

The general object of this invention is to provide press rollers whichovercome the difiiculties encountered with ordinary press rollers byproviding press rollers which will dissipate heat and electricalcharges, and which possess properties to prevent the generation ofkinetic friction.

A more specific object of this invention is to provideelectrically-conductive, non-friction press rollers.

Another object of this invention is to provide a method of producingsuch rollers.

' 3 Gther objects and advantages of the invention will more fully appearfrom the following description.

Since my invention resides in large part in the prop- ;erties andcharacteristics of the coating material of the press rollers, and sincethe art of making rubber-covered rollers is quite old, I do not deem itnecessary to exjplain in detail the physical structure or mechanicalmethod of manufacture of the rollers. Rather, I shall explain theformulations and process for compounding the press rollers of myinvention.

The surface of press'rollers is preferably composed or" someoil-resistant compound, since such rollers are constantly in closeproximity to printing inks Which are formulated with pigments in eitheran oil or an oil varnish vehicle. Were a compound which wasnotoil-resistant used as a surface coating for press rollers, the coating,were it to be covered with ink, would enlarge or expand, giving rise tonew dimcu'lties. It is especially important that inking rollers have an"oil-resistant coating, since normally they are constantly coated withink.

' .It has been discovered through experimentation that certainrubber'and plastic polymers are oil-resistant and Well suited for use asa'base compound in the manufacture of coatings forelectrically-conductive press rollers.

Examples of such compounds are: Teflom silicone; neoprene;nylontirradiated polyethylene; butyl rubber; natural rubber; Hypalonrubber; chlorinated rubber; and

iso-cyanides, such as Vulcallon.

Since the coatings of press rollers are mold-cured upon a mandrel, andsince rubber and plastic polymers should be in a liquid state for moldpouring, natural rubber, when oils and solvents commonly employed in inkvehicles, whereas rubber or plastic which has been vulcanized byperoxide is impervious to these substances.

When sulphur is used as a vulcanizing agent for rubber or plastic, theresulting product consists of molecules of very long chain length withcertain cross-linkages extending from one to the other. so long chainmolecules are easily broken,,as by being subjected to sunlight.

When peroxide is used as a vulcanizing agent for rubber or plastic, theresulting product consists of molecules of shorter chain length and isthus more impervious to oils and solvents and is much more stable,since, as a general rule, the shorter the chain length of a molecule themore stable the molecule. I

A peroxide is a compound containing two monovalent .or bivalent oxygenatoms joined by a single linkage.

When a peroxide is used as. a vulcanizingagent, and the compound inwhich it is used is subjected toheat, the peroxide,'being quiteunstable, decomposes. The: decomposition of the peroxide ischaracterized by a scission of the peroxide at that point in themolecular'st'ructure Whereat the oxygen atoms are joined by a singlelinkage.

7 .As a result of the scission, an oxygen radical is formed.

The oxygen radical joins with a hydrogen atom, as a'free oxygen radical,resulting in the formation of a hydrfoxyl radicali. g t i The hydroxylradical which is formed in a' maiiner I similar to that described aboveis very reactive, and tends to combine with other ingredients nonmallypresent in'the rubber or plastic to form a hydrocarbon radical which, inits simplest form, will combine with another hydrocarbon radicalsimilarly formed to produce a'vulcanite wherein the cross-linkage is adirect carbon-to-oarbon I bond. From experimentation it has beendetermined rnents are' added'thereto in order that the rubber will i iassume those qualities, such as density or hardness, which are desiredfor the specific application for which the rubber is to be employed.

lnthe case of this invention, the pigments added to the base compoundare'responsi-ble for the electrical conductivity of the compound, andhence the type of pigment is critical. Those pigments which are suitedfor use in the manufacture of the roller-coatings of my inventioninclude: carbon blacks, acetylene black, super abrasion furnaoe blacks',ch'annel'blacks and graphite. Of these pigments, acetylene black isideally suited for use in the L rollers of this invention, because itsspatial network' coincidesremarkably well with the spatial network ofthe base compounds'with whichit is formulated. I

In order for the pigments to lend the qualities above referred to to thebase compound with which they are formulated, it is necessary that theybe dispersed evenly throughout the base compound. When theabove-mentioned pigments are to be usedwith depoiy-merized rubber, thesepigments must be suitably prepared in order to assuret-heir dispersiontherein, due to the fact that these pigments are not naturallyhydrophobic, and depolymerized rubber contains a. certain amount or" oilwhich is necessarily added thereto to make it flowable.

It is possible-to coat the pigments with a hydrophobic film, and thusassure their uniform dispersion in depolym- 'e rized rubber; Onemethod'of doing this is to mill said pigments in a water solutioncontaining a primary hydrogenated .tallow amine acetate for about thirtyminutes.

The pigments absorb the formulation and a hydrophobic film is formed onthe pigment particles. 7

To'impart non-friction properties to the rollers, and

thus overcome the efiects of kinetic friction, mica; graph- .1 ite ormolybdenum disulphide may be added thereto.

' The compoud, comprising rubber or plasticpolymers tov rule, thecompound will cure or, Vulcanize in about one gether'with'the' fillersand pigments, ispreferably val 1 canized byperoxide rather thansulphur,since rubber,

which hasbeen vulcanized bysuIphuris not impervious to andasuitable'quantity: of tetra-methyl thiuram disu-lfide l to serve as acuringagent. This mixture 'ismilled together.

hour when subjected to a' temperature of approximately 149 C. for thatperiod of time.

Among the formulations which may be used for the purpose of makingelectrically-conductive, non-friction 7 press rollers, the followingexamples of compounds which I have used may be given:

, Example I 7 I To 7 5 parts of water 5 parts of an amine acetate suchas iosln Amine (dehydroabie tylamine) and" 20 parts of eithen acetyleneblack, super abrasion furnace black 013 graphite are-added. The entiremixtureis dispersed for one'hour in a high-speed colloidal mill.

ucts Company, 50 parts of a pigmenhsuch as acetylene black, which'has'been treated as hereinabove' described and 2 parts of di-tertiarybutylperoxide are milled to- This mixture is mold cured'at-a'temperatureof at least 340 F. under steam pressure equal'to at least pounds persquare inch.

It should be noted that the parts of the constituents referred to. inthis and other examples .mean parts by weight. 1

Example I] To 109 parts of Thiokol rubber, a synthetic made. from thereaction of sodium polysulfide with a chlorinated liydrocarbon, areadded 50 parts of acetylene blackwhich has been treated ln the. mannerdescribedinExample I,

After being sub ected to the colloidal mill, the mixture is'vacuunrgether on a rubber mill. After milling, the mixture may be mold cured ata temperature of at least 340 F. under a steam pressure equal to atleast 110 pounds per square inch.

Example III To 100 parts of neoprene (2 chloro-1,3 butadiene) are added2 parts of Neozone A (phenyl alpha-naphthylamine), 4 parts of magnesia,5 parts of zinc oxide, parts of a hydrocarbon rubber oil, such as Circolight oil, and 50 parts of acetylene black. The mixture is milledtogether on a cold rubber mill. After milling, the mixture may be moldcured at a temperature of at least 287 F. and under steam pressureequal, at least, to 110 pounds per square inch.

Example IV To 100 parts of a synethetic rubber such as Butyl rubber(vulcanizable hydrocarbon polymer of low unsaturation) are added 2 partsof Neozone A, 4 parts magnesia, 5 parts Zinc oxide, 10 parts of ahydrocarbon rubber oil and 50 parts of acetylene black. After milling,the mixture may be mold cured at a temperature of at least 340 F. andunder a steam pressure equal at least to 110 pounds per square inch.

By employing the press rollers of my invention many advantageous resultsmay be realized, among them are: less time need be devoted to cleaningthe press room, since ink misting is eliminated; the presses may beoperated for a longer period of time without being torn down to replacepress rollers, since press rollers made in accordance with my inventiondo not wear out, pit or glaze as readily as ordinary rollers; the inktransfer from one inkingroller to another, when both rollers are made inaccordance with my invention, is more uniform than is the case whenordinary rollers are employed; and improved printing results may beobtained, since wicking of the ink is eliminated.

Since certain changes and variations may of course be made in thestructures, compositions and procedures above-described withoutdeparting from the principles and scope of the invention, it is intendedthat the foregoing specification shall be interpreted as illustrativeand not in a limiting sense.

I claim:

1. A printing press roller comprising a mandrel and a smooth, impervioussurface covering thereon of resilient rubber-like material havingoil-resistant properties, such surface covering being made from acomposition having acetylene black uniformly dispersed therein to renderit electrically conductive and molybdenum disulphide incorporatedtherein to impart non-friction properties thereto.

2. A printing press roller comprising a mandrel and smooth impervioussurface covering bonded thereto, said covering being made of a resilientrubber-like base material having oil-resistant properties, said basematerial having uniformly dispersed therein an electrically-conductivepigment material, taken from the group consisting of acetylene black,carbon blacks, super abrasion furnace blacks and channel blacks, insufficient amount to render said surface covering electricallyconductive, whereby it will dissipate static electrical charges frompaper webs contacting the roller, said base material also havinguniformly dispersed therein a material taken from the group consistingof molybdenum disulphide, mica and graphite, to impart non-frictionproperties to said surface covering, whereby the generation of staticand kinetic friction in the normal operation of the roller will beavoided.

3. A method of producing a printing press roller comprising a mandrelwith a smooth, impervious electrically conductive covering thereon,which consists in applying a hydrophobic film to pigments taken from theclass con sisting of acetylene black, carbon black and super abrasionfurnace blacks, by mixing such pigments in a water solution containingan amine acetate selected from the group consisting of primaryhydrogenated tallow amine acetate and dehydroabietylamine, removing saidpigments from the water solution, drying the pigments preparing acompound containing such pigments and depolymerized rubber with thepigment particles uniformly dispersed in such depolymerized rubber, andapplying said compound to said mandrel in firmly bonded relationship toform said surface covering.

References Cited in the file of this patent UNITED STATES PATENTS1,963,896 Gardner June 19, 1934 2,012,223 Cutler Aug. 20, 1935 2,067,060Minor Jan. 5, 1937 2,088,470 Freedlander July 27, 1937 2,088,471Freedlander July 27, 1937 2,211,592 Castello Aug. 13, 1940 2,219,054Palm et al. Oct. 22, 1940 2,278,982 Frolich Apr. 7, 1942 2,373,876Cutler Apr. 17, 1945 2,393,100 Gallay et al. Jan. 15, 1946 2,420,911Roedel May 20, 1947 2,422,903 Huston June 24, 1952 2,570,935 FreedlanderOct. 9, 1952 2,582,795 Prentiss et al. Jan. 15, 1952 2,597,741 Macey May20, 1952 2,639,276 Smith-Iohannsen May 19, 1953 2,688,576 Ryan et al.Sept. 7, 1954 2,703,768 Hall Mar. 8, 1955 2,709,160 Korejwa et al May24, 1955 2,763,208 Rockoif et al. Sept. 18, 1956 OTHER REFERENCES TheGas 8: Oil Journal, Oct. 6, 1945, Arch L. Foster, pp. 86-88.

Modern Synthetic Rubbers, 3rd edition, London, Chapman & Hall, Ltd.,1949 (only pp. 255, 318, 443, 453, 455, 454, 500).

Chemical and Engineering News, April 24, 1961, pages 121-124.

1. A PRINTING PRESS ROLLER CONSISTING OF A MANDREL AND A SMOOTH,IMPERVIOUS SURFACE COVERING THEREON OF RESILIENT RUBBER-LIKE MATERIALHAVING OIL-RESISTANT PROPERTIES, SUCH SURFACE COVERING BEING MADE FROM ACOMPOSITION HAVING ACETYLENE BLACK UNIFORMLY DISPERSED THEREIN TO RENDERIT ELECTRICALLY CONDUCTIVE AND MOLYBDENUM DISULPHIDE INCORPORATEDTHEREIN TO IMPUT NON-FRIVTION PROPERTIES THERETO.